In almost all water systems such as rivers, lakes, streams, pools, industrial and ornamental water systems, irrigation systems etc., excessive growth of algae, (aquatic) plants and fungi can occur, which can be a severe problem, in particular because it can impart a distastefull appearance and odour to the water, it can interfere with the flow of the water, and may be harmfull to the growth or health of other life.
In the past, various types of algicides and herbicides have been employed in an attempt to control the growth of algae and aquatic plants. For example, dipyridylium compounds, as disclosed in U.S. Pat. No. 2,823,987 have been widely used to control the growth of algae and aquatic plants, and while these compounds have been effective, there are certain varieties of aquatic plants, such as Hydrilla, against which the dipyridylium compounds are relatively ineffective. Moreover, conventional herbicides have relatively little effect against algae.
Since the tun of the century, copper has been known as an effective control on algae, in particular copper sulfate. Not only is it probably one of the most effective chemical algicides it is also safe to use. Also cobalt is know to have algicidal properties. However, the solubility of copper salts such as sulfate salts, is severely affected by increasing alkaline pH's. In waters containing bicarbonates, carbonates and/or a pH over 7, it has long been known that copper sulfate is ineffective because of copper precipitating in the form of copper hydroxide or copper carbonate. Since the algicidal properties of copper sulfate are due to the copper ions, without these toxic copper ions, copper sulfate is essentially hainrmless to algae and the like.
Chelating agents, such as EDTA, have been used in combination with copper ions, to improve its solubility in alkaline environment, as for example described in U.S. Pat. No. 5,407,899 and EP 259,525. The chelating agent releases and maintains the toxic forms of copper, i.e. Cu.sup.++, in the water.
However, the inventors have now found that not all chelating effectively release or maintain the level of dissolved copper ions. They have also found that a chelating agent does not perform effectively in all types of water system.
The inventors have now found that this can be due to the fact that these chelating agents may bind to other metal ions which may be present in the water. It has been found that in particular the presence of calcium ions can reduce the efficiency or effectiveness of certain chelating agents, such as EDTA. The nature of the systems and the methods wherein the chelating agents are used is such, that the presence of calcium ions is unavoidable or even desirable. Thus, this can lead to reduction of the chelating of the copper or cobalt ions, which subsequently can form insoluble salts and are thus no longer effective algicides.
This problem can be even more severe in several applications, where calcium-containing compounds are additionally required as algicides, for example calcium hypochlorite.
However, the inventors have now found that specific complexing agents are excellent complexing agents for forming complexes with the selected metal ions, useful in algicidal, herbicidal, fungicidal compositions, such as copper and cobalt ions, in particular in the presence of calcium ions.